Evidence for a cell-specific negative regulatory element in the first intron of the gene for bovine elastin

Aortopulmonary fistula in a Warmblood mare associated with an aortic aneurysm and supravalvular aortic stenosis

This case report describes the clinical presentation, the necropsy findings, and genetic results of a 13-year-old Warmblood mare presented with colic and a bilaterally loud, holosystolic murmur. Echocardiographic examination revealed the presence of a thoracic aortic aneurysm, an aortic pseudoaneurysm, a periaortic hematoma (circumferential cuffing by perivascular hemorrhage), and aortopulmonary fistulation. A supravalvular aortic stenosis (SVAS) was visible during echocardiography. Necropsy confirmed that the thoracic aortic aneurysm had ruptured and connected to the pseudoaneurysm, which fistulated into the pulmonary artery. Histologically, the aneurysm wall revealed chronic lesions such as fibrosis, mucin depositions, mineralizations, and elastin fragmentation. The mid abdominal aorta showed lesions suggestive of a systemic elastin arteriopathy. Molecular analysis, however, could not attribute this disease to a variant in the elastin gene, the most common causative gene for SVAS. To the authors' knowledge, this case report describes a case of aortopulmonary fistulation in a Warmblood horse associated with the presence of SVAS and an aortic aneurysm.

17β-Estradiol Increases Non-CpG Methylation in Exon 1 of the Rainbow Trout (Oncorhynchus mykiss) MyoD Gene

MyoD is an important myogenic transcription factor necessary for the differentiation of myogenic precursor cells (MPC) to form mature myotubes, a process essential for muscle growth. Epigenetic markers such as CpH methylation are known gene regulators that are important for the differentiation process. In this study, we investigated whether DNA methylation is a potential mechanism associated with the ability of 17β-estradiol (E2) to reduce MyoD gene expression and muscle growth in rainbow trout. Rainbow trout received a single intraperitoneal injection of E2 or the injection vehicle (control). Skeletal muscle was collected 24 h post injection and analyzed for DNA methylation within the MyoD gene and the expression of DNA methyltransferases. CpG islands of the MyoD gene were predicted using MethPrimer software, and these regions were PCR amplified and analyzed using bisulfite sequencing. The percent methylation of the targeted CpG did not differ between control and E2-treated fish. However, percent CpH methylation in the MyoD exon 1 region was elevated with E2 treatment. Two of the methylated CpH sites were located in conserved transcription factor binding motifs, estrogen response element (ERE), and Myc binding site. Quantitative real-time PCR analysis revealed a significant increase in expression of DNA methyltransferases, Dnmt3a and Dnmt3b, in E2-treated muscle, suggesting an increased genome methylation. Differential CpH methylation in MyoD gene of control and E2-treated fish suggests an epigenetic mechanism through which E2 decreases MyoD gene expression and contributes to reduced muscle growth.

Positive transcriptional regulatory element located within exon 1 of elastin gene

Elastin gene transcription is cell type specific and developmentally regulated, but the promoter often exhibits relatively weak activity in transient transfections of cells that express elastin at high levels. To search for positive-acting regulatory sequences, we isolated genomic clones spanning the mouse elastin gene and extensive 5'- and 3'-flanking regions. Restriction fragments of potential regulatory regions were ligated 5' or 3' relative to the active promoter to test for enhancer activity in transient transfections of fetal rat lung fibroblasts, which express elastin at high levels, and distal lung epithelial cells, which do not express detectable elastin. Fragments of intron 1 did not exhibit significant enhancer activity. Inclusion of the 84-bp exon 1 and adjacent 5'-untranslated region increased activity of the elastin promoter approximately sixfold compared with parental constructs. Transfections with constructs of varying promoter length showed that as little as 40 bp of the 5' end of exon 1 confers enhanced activity in elastin-expressing rat lung fibroblasts, but these constructs had variable activity in lung epithelial cell lines. This region, localized between the transcription start site and extending into exon 1, binds Sp1 in nuclear extracts from elastin-expressing cells. These studies indicate a role for the 5' end of the first exon of the elastin gene in regulating strong transcriptional activity in elastogenic cells.

Altered nuclear protein binding to the first intron of the renin gene of the spontaneously hypertensive rat

We and others have reported elevated levels of renin mRNA in extrarenal tissues of the spontaneously hypertensive rat (SHR) of the Okamoto strain. We hypothesise that this is due to mutations we have found in putative, cis-regulatory regions in the first intron of its renin gene. Here we report two G-A mutations at position +502 and +934 of the first intron of the SHR renin gene, when compared to normotensive Wistar Kyoto (WKY) and Sprague Dawley (SD) rats. These mutations fall within consensus sequences for the well described E2A and peroxisome proliferator-activated receptor (PPAR) transcription factors. We used electrophoretic mobility shift assays to determine if these mutations alter the pattern or affinity of nuclear protein binding to oligonucleotides homologous to these regions of the renin gene. Both mutations significantly altered the intensity and pattern of nuclear protein binding to oligonucleotides homologous with the renin gene regions bearing these putative transcription factor binding sites. Thus these mutations have the potential to alter the type and/or affinity of transcriptional factors for the SHR renin gene in vivo, and result in renin overproduction at an extra-renal tissue site subserving blood pressure control.

Nucleotide variations in intron 1 of the renin gene of the spontaneously hypertensive rat

The renin gene is known to be overexpressed in the spontaneously hypertensive rat (SHR) of the Okamoto strain. As the first intron of many genes controls transcription rate, we examined whether the first 1,100 base pairs of the SHR first intron possessed mutations in putative transcriptional factor binding sites. Such mutations might then form the basis for overexpression of the renin gene in the SHR. A BglII restriction fragment length polymorphism (RFLP) was identified in the first 1,100 base pairs of the first intron of the renin gene of the SHR when compared to Wistar Kyoto (WKY) and Sprague Dawley (SD) normotensive rats. Sequence analysis of this region located the BglII RFLP between positions 501-505 of the rat renin gene. The new BglII cut site was produced by a single base mutation from G to A at position 502. While a number of other insertional and deletional events were found in the SHR, WKY and SD sequences over this region, only two were unique to the SHR. These mutations occurred at positions 191, 502, 934 and 1070. The latter three fell within sequence motifs known to bind the transcriptional factors PPAR, E2A and AP2 respectively. Thus we propose that these mutations alter the DNA binding characteristics of one or more transcriptional factors to the SHR renin gene first intron resulting in its overexpression which, in turn, might form the basis for a tissue renin-angiotensin dependent hypertension in this strain.

Regulation of human renin secretion and gene transcription in Calu-6 cells

Calu-6 cells were characterized for studying the transcriptional regulation of the human renin gene. Analysis of cis-acting elements of the renin promoter showed the highest activity within the first 582 bp in serum-free conditions and of the 892 bp in the presence of serum. cAMP activates renin mRNA synthesis parallel to renin production (20-fold increase) as well renin promoter activity (2-fold). cAMP response element and the (-77 to -67) element are both necessary for activation of the renin promoter but do not act independently. Functional analysis of Intron A revealed the presence of a silencer specific to renin-producing cells.

Elements within the beta-lactoglobulin gene inhibit expression of human serum albumin cDNA and minigenes in transfected cells but rescue their expression in the mammary gland of transgenic mice

Two new beta-lactoglobulin (BLG)/human serum albumin (HSA) hybrid gene vectors were constructed and tested for expression in COS-7 cells and in transgenic mice. The HSA sequences were inserted between the second and sixth BLG exons. Transient transfection experiments with these vectors as well as a series of additional vectors with either the BLG 5'- or 3'- intragenic sequences revealed that sequences within BLG exon 1/intron 1/exon 2 abrogated BLG- directed HSA expression in vitro, regardless of the presence of HSA introns or the origin of the 3' polyadenylation signal. In contrast, the same BLG expression cassette enabled the efficient expression of HSA cDNA or minigene in the mammary gland of transgenic mice with subsequent secretion of the corresponding protein into the milk of 56 and 82%, respectively of the mouse strains at levels up to 0.3 mg/ml. Previous attempts to express HSA cDNA inserted into exon 1 of the BLG gene had failed [Shani,M., Barash,I., Nathan,M., Ricca,G., Searfoss,G.H., Dekel,I., Faerman,A., Givol,D. and Hurwitz,D.R. (1992) Transgenic Res. 1, 195- 208]. The new BLG expression cassette conferred more stringent tissue specific expression than previously described BLG/HSA constructs [Barash,I, Faerman,A., Ratovitsky,T, Puzis,R., Nathan,M., Hurwitz,D.R. and Shani, M. (1994) Transgenic Res. 3, 141-151]. However, it was not able to insulate the transgenes from the surrounding host DNA sequences and did not result in copy number dependent expression in transgenics. Together, the in vitro and in vivo results suggest both positive and negative regulatory elements within the BLG intragenic sequences evaluated. The new BLG construct represents an extremely valuable vector for the efficient expression of cDNAs in the mammary gland of transgenic animals.

Novel mutation in the first intron of the spontaneously hypertensive rat renin gene upstream of the tandem repeat element

1. The first 1100 base pairs of the first intron of the renin gene was amplified from the spontaneously hypertensive rat (SHR), Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rats. A Bgl II restriction fragment length polymorphism (RFLP) was identified in this region of the SHR renin gene. 2. Sequence analysis located the Bgl II RFLP between positions 500 and 505 of the reported rat renin gene. The new Bgl II cut site was produced by a single base mutation from G to A. 3. Whether this mutation in the first intron of the SHR renin gene plays a role in the reported overexpression of the renin gene in this strain remains to be elucidated.

Mutations in the first intron of the SHR renin gene disrupt putative regulatory elements

1. Four single base mutations unique to the spontaneously hypertensive rat (SHR) were identified in the first 1100 base pairs of its renin gene first intron when compared to that of Wistar-Kyoto and Sprague-Dawley normotensive rats. 2. These mutations were found to fall within the consensus sequences for a number of transcription factors and thus may alter the affinity of these putative transcription factor binding sites. 3. The reported overexpression of the renin gene in the SHR may therefore result from these structural abnormalities and, in turn, result in a tissue angiotensin-dependent hypertension in this strain.